Problem: Solve for $x$ and $y$ using substitution. ${5x+4y = -4}$ ${x = -2y+10}$
Explanation: Since $x$ has already been solved for, substitute $-2y+10$ for $x$ in the first equation. ${5}{(-2y+10)}{+ 4y = -4}$ Simplify and solve for $y$ $-10y+50 + 4y = -4$ $-6y+50 = -4$ $-6y+50{-50} = -4{-50}$ $-6y = -54$ $\dfrac{-6y}{{-6}} = \dfrac{-54}{{-6}}$ ${y = 9}$ Now that you know ${y = 9}$ , plug it back into $\thinspace {x = -2y+10}\thinspace$ to find $x$ ${x = -2}{(9)}{ + 10}$ $x = -18 + 10$ ${x = -8}$ You can also plug ${y = 9}$ into $\thinspace {5x+4y = -4}\thinspace$ and get the same answer for $x$ : ${5x + 4}{(9)}{= -4}$ ${x = -8}$